Disk drives are an important data storage technology. Read-write heads directly communicate with a disk surface containing the data storage medium over a track on the disk surface.
FIG. 1A illustrates a typical prior art hard disk drive, which may be a high capacity disk drive 10. Disk drive 10 includes an actuator arm 30 that further includes a voice coil 32, actuator axis 40, suspension or head arms 50. A slider/head unit 60 is placed among data storage disks 12.
FIG. 1B illustrates a typical prior art high capacity disk drive 10. The actuator 20 includes actuator arm 30 with voice coil 32, actuator axis 40, head arms 50, and slider/head units 60. A spindle motor 80 is provided for rotating disk 12.
Since the 1980's, high capacity disk drives 10 have used voice coil actuators 20 to position their read-write heads over specific tracks. The heads are mounted on head sliders 60, which float a small distance off a surface 12-1 of a rotating disk 12 when the disk drive 10 is in operation. Often there is one head per head slider for a given disk surface 12-1. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator 20 for positioning head arms 50.
Voice coil actuators 20 are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move head arms 50 to position head slider units 60 over specific tracks. Actuator arms 30 are often considered to include voice coil 32, actuator axis 40, head arms 50, and swage mounts 70. Swage mounts mechanically couple head sliders 60 to actuator arms 50. Actuator arms 30 may have as few as a single head arm 50. A single head arm 52 may connect with two head sliders 60 and 60A (as shown in FIG. 1B).
FIG. 1C illustrates a cross sectional view of a single platter prior art disk drive 10 and FIG. 1D illustrates a cross sectional view of a double platter prior art disk drive 10. Each disk drive 10 includes a disk base 100 and cover 110 that encloses disks 12 that are rotated by the spindle motor 80.
Read-write head positioning errors are a significant point of failure and performance degradation. Positioning errors are caused in part by disk fluttering. Disk fluttering occurs when a disk flexes, or vibrates, as it rotates. Some fluttering problems for disks are due to instabilities in the motor turning the disk. Fluttering problems of this type are usually addressed by spindle motor manufacturers.
There have been attempts to address disk flutter problems in the prior art. U.S. Pat. No. 6,239,943 B1, entitled “Squeeze film dampening for a hard disc drive” is directed to an attempt to address disk flutter problems. This patent discloses “a spindle motor . . . cause[ing] rotation of . . . a single or multiple disc or stack of disks . . . mounted in such a way that the rotating bottom or top (or both) disc surface is closely adjacent to a disc drive casting surface. The squeeze film action in the remaining air gap provides a significant dampening of the disc vibration. . . . Typical implementations use air gaps of 0.004–0.006″[inch] for 2½ inch [disk] drives and 0.006–0.010″[inch] for 3½ inch [disk] dirves” (lines 12–21, column 2). “According to the theory presented . . . , the damping provided by the squeeze film effect between the disc and base plate should not be a function of the spinning speed.” (lines 53–55, column 5). “Significant reduction in the vibration of the top disc, in a two disc system, can be achieved by supplying squeeze film damping to the bottom disc alone. This is important because in a practical design, damping discs other than the bottom disc may be difficult.” (line 65 column 5 to line 2 column 6).
While the inventors are respectful of U.S. Pat. No. 6,239,943, they find several shortcomings in its insights. It is well known that the combined relationship of read-write heads on actuators accessing disk surfaces of rotating disks brings operational success to a disk drive. There are significant aerodynamic forces acting upon a read-write head assembly and its actuator due to the rotational velocity of the disk(s) being accessed. These significant aerodynamic forces acting upon the actuator, the read-write head, or both, are unaccounted for in the cited patent. There are also significant gap distances that may relate to rotational velocity which are unaccounted for in the cited patent, as well as the inventors' experimental evidence indicating larger air gap providing reductions in track position error than this patent or any other prior art accounts for. There are significant insights to be gained from seeing the development of wave related phenomena in the physical system, both acoustically and mechanically, which are unaccounted for in the cited patent.
Increased recording density and increased spindle speeds are key factors to competitiveness in the disk drive industry. As recording densities and spindle speeds increase, both head positioning accuracy and head-flying stability must also increase. However, as spindle speeds increase, air flow-induced vibrations may also increase which may result in larger amplitude vibrations of the head-slider suspension causing read-write head positioning errors. Additionally, air flow-induced vibrations acting upon a rotating disk cause disk fluttering, which contributes to track positioning errors. Thus, reducing air flow-induced vibration is essential to reducing head-positioning and read-write errors.